There is known an electromagnetic actuator that drives a plunger by a magnetic force generated through energization of a coil to operate an external device through a rod that is formed integrally with the plunger. For example, an electromagnetic actuator of the patent literature 1 is used to operate an oil pressure control valve of a valve timing adjuster device of an engine.
In the patent literature 1, the rod projects from the plunger in an axial direction. An outer peripheral surface of the rod is parallel with a central axis. A yoke forms a support portion that includes a through-hole, through which the rod is received.
When the rod is moved in the axial direction, the rod is slid along an inner wall surface of the through-hole of the support portion. At this time, when a friction force is large, wearing between the rod and the support portion may be increased, and there is a possibility of causing an immovable state of the rod, i.e., a possibility of occurrence of forced fitting of the rod against the inner wall surface of the through-hole. One countermeasure against this disadvantage may be increasing of a clearance between the rod and the inner wall surface of the through-hole.
When the amount of electric power supplied to the coil is increased, the magnetic force is increased. In response to the increase in the magnetic force, a projecting length of the rod, which projects from the support portion, is increased, and a force (side force), which is applied to the plunger in a radial direction, is increased. Therefore, the amount of swing of a distal end of the rod in the radial direction is disadvantageously increased when the projecting length of the rod, which projects from the support portion, is increased. One countermeasure against this disadvantage may be reducing of the clearance between the rod and the inner wall surface of the through-hole.
Therefore, it is obvious that the above two countermeasures are contradictory to each other. Specifically, when the size of the clearance is increased to reduce the frictional force between the rod and the support portion, the amount of swing of the distal end of the rod in the radial direction is disadvantageously increased. Furthermore, when the size of the clearance is reduced to reduce the amount of swing of the distal end of the rod in the radial direction, the frictional force between the rod and the support portion is disadvantageously increased.